There is no "speedometer becoming illegal" issue in the US. I ran 265/65/17 for snows. I think 265/70/17 would not have enough clearance.255/65-17 or 235/70-17 are as high as you can go without the speedometer becoming illegal.
265/70-17 will give a 5% under-read on the speedometer.
Maybe for the manufacturer, but once you drive it off the lot, you can put on whatever size tires fit.I thought that the US was a signatory to the UNECE international standards - it's a pre-requisite to any world trade deal such as the US is pushing for at the moment.